... 4 Recent advances have also been made in catalytic asymmetric alkylation, particularly as applied to α-amino acid synthesis. ... 4 R 1, R 2 X, dr a, yield (%), product. a CH 3, CH 2 CHCH 2 Br, 49:1, 90, 7. a CH 3, PhCH 2 Br, 99:1, 89 b, 8. a CH 3, PMBOCH 2 CH CHCH 2 I, 99:1, 70, ...